Computed Radiography에서 Additional Filtration Material에 따른 Radiation Dose와 Image Quality의 변화
Changes of Radiation Dose and Image Quality Due to Additional Filtration Material in Computed Radiography
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초록
필터는 저에너지 X선을 흡수함으로써 평균에너지를 증가시키고, 환자의 피폭선량을 감소시키는 작용을 한다. 본 연구는 Mo과 W 등의 재질이 디지털 방사선영상장치인 CR에서도 사용이 가능한지 SNR, FOM, histogram 등의 영상평가와 선량 측정을 통해 확인하였다. 또한 필터의 재질에 따른 선질측정과 함께 관전압의 변화에 따른 적합한 필터 조합을 찾아보았다. 피부입사선량은 Mo필터가 Cu필터에 비해 42~56%까지 선량 경감효과가 있었고, 투과선량도 Mo필터가 Cu필터보다 1.5배 정도 높게 나타났다. 영상 평가에서 W은 필터로 사용함에 부적절하였으나, Mo은 80kVp 이상의 관전압에서 영상의 질을 저하시키지 않으면서 선량을 감소시킬 수 있는 필터로 충분히 사용할 수 있음을 확인하였다. 2.0mmAl+0.1mmMo은 관전압이 높아질수록 2.0mmAl+0.2mmCu와 histogram width가 거의 같아서, 비교적 높은 관전압인 80, 100, 120kVp에서는 Mo필터의 사용이 가능하다. 2.0mmAl+0.1mmMo의 SNR은 2.0mmAl+0.2mmCu와 2.0mmAl+0.1mmCu의 SNR과도 큰 차이가 나지 않았다. 따라서 디지털 방사선 영상 중 80kVp 이상을 이용하는 일반촬영에서 Cu를 대신하여 Mo을 필터로 사용하면 Cu에 비해 영상의 질을 저하시키지 않으면서 환자의 피폭선량을 크게 감소시킬 수 있으므로, 실제 임상의 흉부 촬영 및 고관전압 촬영 등에 충분히 적용할 수 있다고 본다.
Abstract
Filter absorbs low-energy X-ray to increase the average energy and reduces patient exposure dose. This study investigates if the materials of Mo and W could be used for the digital imaging device CR by conducting image assessment and dose measurement of SNR, FOM and histogram. In addition, measurement of beam quality was conducted depending on the material of the filter, and at the same time, a proper combination of filters was examined depending on the change in tube voltage (kVp). In regard to entrance skin dose, Mo filter showed the dose reduction by 42∼56%, compared to Cu filter. Moreover, Mo filter showed higher transmission dose by around 1.5 times than that of Cu filter. In image assessment, it was found that W was unsuitable to be used as a filter, whereas Mo could be used as a filter to reduce dose without decline in image quality at the tube voltage of 80 kVp or higher. As tube voltage increased, 2.0mm Al+0.1mm Mo almost had a similar histogram width to that of 2.0mm Al+0.2mm Cu. Therefore, Mo filter can be used at relatively high tube voltage of 80kVp, 100kVp and 120kVp. The SNR of 2.0mm Al+0.1mm Mo did not show any significant difference from those of 2.0mm Al+0.2mm Cu and 2.0mm Al+0.1mm Cu. As a result, if Mo filter is used to replace Cu filter in general radiography, where 80kVp or higher is used for digital radiation image, patient exposure dose can be reduced significantly without decline in image quality, compared to Cu filter. Therefore, it is believed that Mo filter can be applied to chest X-ray and high tube voltage X-ray in actual clinical practice.
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